BRASILIA, Brazil  Brazil's president Thursday decreed the creation of one of the world's largest environmental protection areas in the Amazon to combat illegal logging and rising violence after the killing of a prominent U.S. human rights activist.

President Luiz Inacio Lula da Silva signed the plan to safeguard the most threatened area of Brazil's Amazon rain forest after U.S. nun Dorothy Stang, 74, was killed there Saturday by gunmen with suspected links to illegal loggers.

The murder of Stang sparked an international outcry to stop death squad activities and deforestation in the Amazon.

Lula said he would not allow powerful timber mafias to threaten his government. He set aside an area three times the size of Belgium for conservation and for restricted logging to block their advance on the world's largest rain forest.

"This is the most important package of measures for the Amazon in Brazil's history," said Nilo D'Avila, the Amazon coordinator for the environmental group Greenpeace, which was among dozens of organizations calling for action. "It's very sad a person has to die, a person as important as Sister Dorothy, for the government to take such a big decision."

The 32,000 square-mile protection area decreed by Lula spans the states of Para, Mato Grosso and Rondonia on the western side of the BR 163 highway -- an access route to the forest for illegal loggers and settlers.

Lula banned use of the BR 163 forest protection area for six months until controlled logging and reserves are set up.

Farther east in Para, the government created conservation areas covering 1,500 square miles -- about the size of the state of Rhode Island.

One of the reserves, known as the Terra do Meio, is in the Trans-Amazonian highway region where Stang was gunned down as she defended small farmers at a government settlement project.

Activists say Amazon violence will escalate unless the government clamps down on loggers and landowners who use gunmen and militias to control rain forest areas.

CRIME CRACKDOWN

Thousands of landless peasants blocked four highways in southern Para Thursday to protest the murder of a union leader and two rural workers since Stang's death.

Few people are punished for such crimes in a region where police and judges are often accused of being in league with landowners.

Lula has sent federal police and 2,000 jungle-warfare troops into the state to find Stang's killers and impose law and order in what is considered Brazil's biggest crackdown on rain forest crime.

Brazil has some of the most rigorous environmental laws in the developing world. It struggles to enforce them in the continent-sized country with a cash-strapped government and agricultural and business elites that often regard protection efforts as a barrier to progress.